Which issue(s) does this change fix?

Why is this change necessary?

AppBuilder require region in sam config to detect deployed stack.
This change allow user to easier swtich to Appbuilder when deployed from SAM CLI

How does it address the issue?

Region is added to default samconfig.toml if user used
sam deploy --save-param

What side effects does this change have?

The Region is only populated but not read by sam cli

Mandatory Checklist

PRs will only be reviewed after checklist is complete

• Add input/output type hints to new functions/methods
• Write design document if needed (Do I need to write a design document?)
• Write/update unit tests
• Write/update integration tests
• Write/update functional tests if needed
• make pr passes
• make update-reproducible-reqs if dependencies were changed
• Write documentation

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.